Field of the Invention
The present invention generally relates to a method of reforming an insulating film deposited on a substrate having a recess pattern, particularly reforming a portion of the film deposited on sidewalls of the recess pattern.
Description of the Related Art
A SiO2 film deposited by plasma-enhanced atomic layer deposition (PEALD) is widely used in the Semiconductor manufacturing industry, since the conformality of such a film is very high, e.g., 100%, when being deposited in a trench having an aspect ratio of about 10. This film profile is important to fabrication processes such as a process of pattern transfer and target etching using spacer-defined double patterning (SDDP), wherein forming vertical spacers with accurate dimensions is important to improve resolution. However, even though a film deposited by PEALD has a high conformality, the quality of the film is not uniform throughout the film and varies depending on the geometrical location of a portion of the film. That is, a portion of the film deposited on a top surface typically has high quality, whereas a portion of the film deposited on sidewalls of a trench typically has poor quality. The poor quality of the sidewall portion of the film becomes a problem when forming a vertical spacer in the process of SDDP, for example, wherein the film deposited by PEALD on a recess pattern of a substrate is subjected to etching to remove portions of the film deposited on a top surface and on a bottom surface of the recess pattern, leaving a portion of the film deposited on sidewalls of the recess pattern, so as to form vertical spacers which are used as a mask to transfer a pattern to a template. Since the mask is subjected to etching, the sidewall portion of the film is required to have good quality such as resistance to wet etching. As such, the quality of the sidewall portion of a film is often important to patterning processes having recesses. For example, in a FinFET device, a gate oxide formed along the surfaces of trenches (including sidewalls thereof) having a high aspect ratio must have high quality. PEALD uses a plasma containing ions which have directionality (anisotropy), and thus, insufficient ion bombardment occurs on sidewalls of a trench, and as a result, the quality of a portion of the film deposited on the sidewalls is inferior to that of a portion of the film deposited on a top surface or bottom surface of the trench.
In order to improve the quality of a sidewall portion of a film, various surface-reforming processes have been developed such as those disclosed in U.S. Pat. No. 8,647,722, and No. 8,722,546. However, as miniaturization of a recess pattern becomes more prevalent, it becomes more difficult to obtain a film having satisfactory profiles, particularly, satisfactory quality of sidewall portion of the film.
Any discussion of problems and solutions in relation to the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion was known at the time the invention was made.